使用 ctypes 创建 python 模块

Question

I have a C library with only two functions: char *foo_decode(const char*) and const char *foo_version() .

I now want to create a python module that allows to call these two functions.

The C library is compiled into foo.so .

This is my python module file:

$ cat foo.py
import ctypes as ct

_lib = ct.cdll.LoadLibrary("./foo.so")
_lib.foo_decode.argtypes = [ct.c_char_p]
_lib.foo_decode.restype = ct.c_char_p
_lib.foo_version.argtypes = []
_lib.foo_version.restype = ct.c_char_p

def decode(fooText):
    return _lib.foo_decode(fooText.encode('utf8')).decode('utf-8')
    
def version():
    return _lib.foo_version().decode('utf-8')

I followed this tutorial .

When I start a python3 interpreter and execute this manually. Everything works fine. I can call the functions and I get back the expected result.

But when I import my module file ( import foo ) I get the error ImportError: dynamic module does not define module export function (PyInit_foo) .

What is happening and what should I do to fix this problem?

My goal is to produce a package downloadable with pip install. Am I on the right track? I don't want wheels since the code is small and has no dependencies. I should thus compile fast and should be very portable.

Answer 1

You have a shared library foo.so and a module foo.py . When Python does import foo it loads only one of them; in your case it's foo.so ; but foo.so is not a Python module hence the error.

Rename your foo.py to something different like foo_wrapper.py and try import foo_wrapper .